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Mice given both an anti-inflammatory drug (also called an NSAID, non-steroidal anti-inflammatory drug) and a selective serotonin reuptake inhibitor (SSRI, a type of antidepressant) scored worse on a test measuring antidepressant effectiveness than mice given only the SSRI, researchers found.

SSRIs, a drug category that includes Prozac, are one of the most widely prescribed antidepressant medications, though the treatment is not effective for everyone, said the study's lead author, Jennifer Warner-Schmidt, a researcher at The Rockefeller University in New York City.

"And there's this long therapeutic delay — you may need to take them for weeks or months, and even then some people don’t respond to them," Warner-Schmidt told MyHealthNewsDaily. "What our data suggest is anti-inflammatory drugs may be one possible preventable reason for that treatment resistance."

More research is needed to determine the exact amount of anti-inflammatory drugs that counteract the SSRI antidepressants. While it's probably safe for a person on SSRIs to pop an Advil for a headache, continued use of anti-inflammatory medications like ibuprofen, aspirin and naproxen — use that may be seen in someone who suffers from chronic pain or arthritis — could counteract the effectiveness of the SSRI, she said.

The study was published online this week in the journal Proceedings of the National Academy of Sciences.

In animals and humans
Warner-Schmidt and her colleagues gave mice an SSRI antidepressant and anti-inflammatory drugs and evaluated their performance on mobility tests. Because it's impossible for mice to say for themselves if the drug improved their mood and emotions, researchers used mobility tests, such as swimming, to see the effect of the antidepressant on the mouse.

On the antidepressant alone, mice experience a 50 to 60 percent increase in mobility, she said. But the anti-inflammatory drugs counteracted the antidepressants to the point where there was no longer a statistically significant improved result on the mobility tests, she said.

"So you could basically say that there was no effect of the SSRI at all with the ibuprofen," she said.

Then, researchers looked at past data from 1,546 people on antidepressants who participated in the 12-week STAR*D study. The STAR*D study asked participants to report their anti-inflammatory drug use, though it did not ask them to specify how frequently or how long they used those drugs.

Researchers found that SSRI antidepressants were about 55 percent effective among people who did not take anti-inflammatory drugs, but only 40 percent effective among those who did.

Study strength
The strength of the new study comes from the combination of both the study in mice and the evaluation of data from a study in humans, Warner-Schmidt said.

"Either standing on its own would not necessarily be as strong," she said, "but because we see in both animals and clinical data, it suggests that people should consider [the findings] if they're not responding well to their SSRIs."

Though more research is needed, researchers said the anti-inflammatory medications could counteract the antidepressants by inhibiting the production of a particular signaling protein, called p11.

SSRIs increase the level of those proteins in the body, so anti-inflammatory drugs could be blocking that effect, Warner-Schmidt said.

Next, Warner-Schmidt said she hopes to do a placebo-controlled study in humans to see if the same effect observed in the mice also occurs in humans.

Pass it on: Common anti-inflammatory drugs, like ibuprofen and aspirin, could counteract the effects of certain antidepressant medications.